The present invention relates generally to the field of reducing electromagnetic emissions, and more specifically to reducing electromagnetic emissions in an LCD display or the like.
Active-matrix liquid-crystal displays (LCDs) and other similar displays with modulated back plane voltages radiate significant energy at harmonics of the modulation rate. For example, in an aviation environment having an avionics display, such emissions can adversely interfere with flight control and display functions, thereby creating a potential dangerous situation for crew and passengers. Attempts to combat this problem have generally involved either filtering the radiation through the addition of a transparent conductor over the display front that acts as an EMI shield, or minimizing the radiated energy by filtering the actual back plane modulation voltages. The transparent conductors are very costly, increase specular reflection, and require special conductive gaskets that are difficult to install, maintain, and test. Filtering the modulation voltages has limited effectiveness due to the need to drive a large capacitive load and the charge times imposed for proper LCD operation. Reducing the modulation frequency is beneficial, but is limited due to the visible optical changes it induces. In many devices, performance specification deviations are required.